1. Field of the Invention
The present invention relates to an analyzer constituted by gas chromatograph combined with inductively coupled plasma mass spectrometer.
2. Description of the Related Art
An analyzer constituted by gas chromatograph combined with inductively coupled plasma mass spectrometer (the gas chromatograph may also be referred to hereinafter as “GC,” the inductively coupled plasma mass spectrometer as “ICP-MS,” and the analyzer constituted by gas chromatograph combined with inductively coupled plasma mass spectrometer as “GC/ICP-MS”) is used with appreciation as an analysis system (Patent Literature 1, Patent Literature 2, Patent Literature 3, and Patent Literature 4).
The target component of analysis is first introduced to the GC in a state dissolved in an organic solvent. Hexane, toluene and other hydrocarbon-based organic solvents are generally used as this organic solvent. The organic solvent is thermally decomposed in argon plasma inside the ICP-MS to become carbon, which then deposits around the orifices of the sampling cone and skimmer cone of the ICP-MS. This presents a problem because the orifice diameters are gradually reduced and the analysis sensitivity drops as a result.
Traditionally, carbon deposition caused by the above reason has been suppressed by a method where oxygen supplied from an oxygen cylinder is constantly introduced through a makeup gas supply line (Non-patent Literature 1), or another method where the ICP torch position is moved away from the sampling cone after a specific number of analysis sessions and air is introduced to ICP to burn, by means of oxygen in air, the carbon deposited around the orifices (Non-patent Literature 2).
However, the methods described in Patent Literatures 1 to 4 above cannot prevent carbon deposition, while the method described in Non-patent Literature 1 requires additional equipment such as an oxygen cylinder, oxygen gas supply line, flow rate controller and mixer, thus making the system complex. The method described in Non-patent Literature 2 requires no additional equipment, but it makes the operation cumbersome and the analysis accuracy also drops because the torch position is moved. All of these GC/ICP-MS apparatuses have been unable to effectively prevent carbon deposition caused by the analysis sample.    [Patent Literature 1] Japanese Patent No. 2931967    [Patent Literature 2] Japanese Patent Laid Open No. 2002-350402    [Patent Literature 3] Japanese Patent Laid Open No. 2004-158314    [Patent Literature 4] Japanese Patent Laid Open No. 2006-38729    [Non-patent Literature 1] J. C. Van Loon, L. R. Alcock, W. H. Pinchin, J. B. French: Spectroscopy Letters, 19 (10), 1125-1135 (1986). Description in Abstract: “Oxygen gas (about 20% of the total sample gas flow) must be injected, into the GC effluent entering the torch, to prevent carbon buildup on the torch.”    [Non-patent Literature 2] N. S. Chong, R. S. Houk: Applied Spectroscopy, 41 (1), 66-74 (1987). Description on p. 67: “One could remove the carbon deposit by displacing the torch laterally to bring about spontaneous oxidation of carbon by air on the hot sampler cone.”